Congenital heart defects (CHDs) are the most common birth defects affecting 8-10 of every 1,000 live births. Although CHDs are associated with significant morbidity and mortality their etiology is mostly unknown, and few primary prevention strategies exist. Approximately 85% of CHDs are nonsyndromic and result from a complex interplay between genetic, environmental, and metabolic influences. Based on our recent discovery that women with CHD-affected pregnancies exhibit alterations in homocysteine and glutathione metabolism, we hypothesize that CHDs are associated with maternal oxidative stress, due to pro-oxidant lifestyle factors and genetic variants that result in altered folate-homocysteine metabolism, and glutathione antioxidant defense capacity. We further hypothesize that the metabolic alterations will be associated with increased frequency of genetic polymorphisms that functionally affect homocysteine and glutathione metabolism. Using genotype data generated from Phase I and Phase II of the International HapMap Project, the investigators will select a highly informative set of haplotype tagging SNPs (htSNPs) in 61 candidate genes encoding for critical enzymes in the folate, homocysteine, and transsulfuration pathways. Selected htSNPs will be genotyped in a large collection of DNA samples from participants in the National Birth Defects Prevention Study. The investigators will determine the association between CHDs and maternal and fetal genetic variants of candidate genes. Independent and modifying effects of pro-oxidant lifestyle factors, including preconceptional maternal obesity, smoking and alcohol will be characterized. In parallel, we will establish whether maternal metabolites among women with CHD-affected pregnancies exhibit evidence of oxidative damage and increased vulnerability to oxidative stress. Coupling metabolic studies with the capacity for high throughput genotyping and powerful new statistical approaches affords an unprecedented opportunity to characterize metabolic, genetic and environmental causes of CHDs. The outcome of this project will be immediate and direct contributions to the understanding of genetic, environmental, and metabolic causes of CHDs and the necessary foundation for clinical and public health primary prevention programs. The convergence of a large-scale case-control infrastructure, advances in genomic tools, and leading multidisciplinary expertise promises to produce a preconception metabolic and genetic profile that can be the basis of a primary prevention program. Successful completion of the proposed studies will advance translational research targeting these costly and devastating birth defects.